Assuming you now have good health, whether or not you should buy health insurance depends on your age. If you're middle-aged (in your 40s), the premiums might not be so high. But if you're older (above 60), the premiums are very expensive.
I've lived in Thailand for over 20 years and have gone to both private and public hospitals. I have found the public hospitals very good, but they often require you to spend the whole day there just to see a doctor. But their fees for us, non-Thais, are very low, I'd estimate only 10% of what a private hospital charges.
I'm 79 now and don't have any health insurance, but feel confident that if/when I need medical attention, a public hospital will be able to provide me the care I need.